Sorption models in cyclodextrin polymers: Langmuir, Freundlich, and a dual-mode approach.

The classic Langmuir and Freundlich sorption models and a dual-mode approach have been tested to study the sorption of aromatic molecules onto beta-cyclodextrin polymers as well as onto analogous sucrose polymers, obtained using the same crosslinking agents (epichlorohydrin, succinyl chloride, toluene diisocyanate, and hexamethylene diisocyanate). The host-guest interaction of the sorbate within the cyclodextrin cavities corresponds to the hole-filling mechanism considered in the dual-mode approach, while the polymer crosslinking networks are capable of entrapping more sorbate molecules via partition. In some cases, when the sorption is governed by the inclusion within the cyclodextrin moieties, a simple Langmuir isotherm fits the data properly. The classic Freundlich equation is also appropriate when phenol is the sorbate because its interaction with beta-cyclodextrin is less specific than that of 1-naphthol.